Real image viewfinder employing roof-type reflecting mirror assemblies

ABSTRACT

A viewfinder utilizing two roof-type reflecting mirror assemblies as an erecting system to produce an erect image wherein the roof-type reflecting mirror assemblies are hollow right prisms whose inner hypotenuse face or two side faces are made into the reflecting surfaces and respectively mounted on suitable apertured plates which are connected to an intermediate apertured plate so that the combinations of these assemblies may deviate the beam of light in a similar manner as the prisms. Wide and brilliant field and high magnification may be attained.

United States Patent Ataka 1 Sept. 12, 1972 [54] REAL IMAGE VIEWFINDER 3,250,195 5/1966 Maitani ..95/42 EMPLOYING ROOF-TYPE 3,257,923 6/1966 Maitani ..95/42 REFLECTING MIRROR ASSEMBLIES Hisanori Ataka, Kawasaki, Japan Assignee: Ricoh Co., Ltd.,

Filed: Sept. 4, 1970 Appl. No.: 69,535

Inventor:

Tokyo, Japan Foreign Application Priority Data Sept. 5, 1969 Japan ..44/83927 US. (21.; ..88/1.5 R, 95/11 v Int. Cl. ..G03b 13/02 field of Search; ..88/l.5 R; 95/42, 11 V References Cited UNITED STATES PATENTS Dittmann ..95/42 Back ..95/42 Primary Examiner-Ronald L. Wibert Assistant Examiner-F. L. Evans Attorney-Henry T. Burke, Robert Scobey, Robert S. Dunham, P. E. Henninger, Lester W. Clark, Gerald W. Griffin, Thomas F. Moran, R. Bradlee Boal and Christopher C. Dunham [57] ABSTRACT A viewfinder utilizing two roof-type reflecting mirror assemblies as an erecting system to produce an erect image wherein the roof-type reflecting mirror assemblies are hollow right prisms whose inner hypotenuse face or two side faces are made into the reflecting surfaces and respectively mounted on suitable apertured plates which are connected to an intermediate apertured plate so that the combinations of these assemblies may deviate the beam of light in a similar manner as the prisms. Wide and brilliant field and high magnification may be attained.

10 Claims, 11 Drawing Figures P'ATE'NTEDSEP 12 m2 SHEE-I 1 BF 4 I PRIOR ART' 2 PRIOR ART FIG. 3A

FIG. 38

INVENTOR. HASMMF/ 4774/64 --'7 M PAIENTEBsEP 12 m2 SHEET 3 OF 4 220 FIG. 8B

I VE N TOR. Hum/0H AMA ,4

REAL IMAGE VIEWFINDER EMPLOYING ROOF- ms REFLECTING MIRROR ASSEMBLIES BACKGROUND OF THE INVENTION The present invention relates to a viewfinder for cameras and more particularly a real image erecting viewfinder employing roof-type reflecting mirror assemblies.

In general, the conventional viewfinder for cameras uses two Porro prisms which are placed together with their vertex edges at right angles with each other to form an erecting system to produce an erect image. However, the prisms are in general expensive, bulky and heavy in weight and produce optical aberrations especially when the material of prisms have strain.

SUMMARY OF THE INVENTION The present invention was made in order to over- .come the difficulties of the conventional viewfinder for cameras employing the prisms. Instead of prisms, the present invention utilizes two roof-type reflecting mirror assemblies. In this specification, a roof-type reflecting mirror assembly is a hollow right prism of which the inner hypotenuse face or the two inner lateral or side faces are made into the reflecting surface so as to displace the beam of light. When the hypotenuse face is a reflecting mirror, the side or lateral faces are opened optically while when the lateral or side faces are used as reflecting mirrors, the hypotenuse face is optically opened. A viewfinder in accordance with the present invention may become compact in size, light in weight and inexpensive to manufacture.

Furthermore, since condenser lenses, an aperture frame, an optical system for viewing the pointer of an exposure meter together with the image of a subject, etc. may be incorporated within an erecting system comprising the roof-type reflecting mirror assemblies of the type described, the viewfinder as a whole may be made more compact in size and light in weight, and a wide field and high magnification may be attained in a simple manner as compared with the conventional viewfinder in which it is impossible to incorporate the optical elements within an erecting system.

Since the plates for mounting the optical elements of a viewfinder such as a field lens, an eye lens, condenser lenses, reflecting mirrors or the like, an aperture frame, etc. may be molded from a synthetic resin, the assembly is much facilitated and the cost is much reduced as compared with the conventional viewfinder.

Furthermore, in a viewfinder in accordance with the present invention, illumination across the field is very brilliant and the frame is not blurred. A further advantage lies in the compactness of a camera incorporating a viewfinder of the present invention.

The invention will become more apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view illustrating the fundamental optical system of a viewfinder for cameras;

FIG. 2 is a diagrammatic view illustrating the optical system of a typical conventional viewfinder system based upon the optical system shown in FIG. 1;

FIGS. 3-A and 3-B are diagrammatic perspective views illustrating the erecting systems which comprise the prisms and are used in the conventional viewfinder systems;

FIG. 4 is a perspective exploded view of a first embodiment of a viewfinder in accordance with the present invention;

FIG. 5 is a sectional view thereof;

FIG. 6 is a diagrammatic sectional view of an alternate embodiment of the present invention through which a pointer of an exposure meter may be viewed togetherwith an image of a subject;

FIG. 7 is a perspective view of an intermediate frame of a further embodiment of the present invention; and

FIGS. 8-A, 8-B and 8-C are top, front and perspective exploded views of another embodiment of the present invention of the type for displacing the beam of light vertically.

PRIOR ART FIG. 1 shows the fundamental optical system of a real image viewfinder comprising a field lens 1, a condenser 2, an erecting prism 3 and an eye lens 4. The lenses 1, 2 and 4 are converging lenses and the image 0 of an image 0 formed by an objective (not shown) is formed by the viewfinder.

FIG. 2 shows an optical system of a typical conventional viewfinder employing a field lens system comprising two positive meniscus single lenses 1a and 1b, a condenser or relay train comprising lenses 2a, 2b and 2c, an erecting prism 3 and an eye lens 4. The erecting prism 3 may be a Porro second type erecting prism such as shown in FIG. 3-A but an erecting system comprising two Porro prisms as shown in FIG. 3-B may also be used. The lenses used in this viewfinder are all meniscus single lenses which may be produced at less cost, but the erecting prism 3 is expensive, bulky and heavy in weight and produces optical distortions or aberrations especially when the material of the prism has strain.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To overcome the problems encountered in the conventional viewfinder of the type described, the present invention employs roof-type reflecting mirror assemblies each having two opposed reflecting surfaces or mirrors as described in more detail hereinafter.

FIRST EMBODIMENT, FIG. 4 AND FIG. 5

The first embodiment of the present invention illustrated in FIG. 4 and FIG. 5 generally consists of a field lens plate 5, an intermediate plate 9 and an eye lens plate 12. The field lens plate 5 has a lens barrel 6 for mounting a field lens 7 and a right-angle-roof type reflecting mirror assembly 8. Both the lens barrel 6 and the reflecting mirror assembly 8 may be made integral with the field lens plate 5. The inner surfaces 8a and 8b of the assembly 8 which intersect at a right angle with each other are made into reflecting surfaces or mirrors by any suitable method such as vacuum deposition.

The intermediate plate 9 is provided with two circular apertures and 9b for mounting condenser lenses 10a and 10b respectively and a rectangular aperture 90 for mounting an aperture frame 1 1.

The eye lens plate 12 is similar in construction to the field lens plate 5 as is readily seen from FIG. 4. A lens barrel 13 for mounting an eye lens and a right-angleroof type reflecting mirror assembly 14 having the reflecting surfaces 14a and 14b are made integral with the plate 12.

The field lens, intermediate and eye lens plates 5, 9 and 12 are assembled as shown in FIG. 5 by means of an adhesive agent or setscrews.

The two roof type reflecting mirror assemblies assembled as shown in FIG. 5 function in a similar manner to the two Porro prisms which are placed with their vertex edges at right angles to each other to form an erecting system to produce an erect image.

SECOND EMBODIMENT, FIG. 6

A small aperture 8ba may be formed through one reflecting surface or mirror 8b of the reflecting mirror assembly 8 of the field lens plate 5 so that a pointer 16a of an exposure meter placed in opposed relation with the aperture 81x; may be viewed together with the image of a subject, thereby facilitating the operation of acamera.

THIRD EMBODIMENT, FIG. 5 AND FIG. 7

In the third embodiment, upstanding portions 9d and 9e perpendicular to the surfaces of the intermediate plate 9 are provided for mounting condenser lenses 10d and 10e respectively so that they may be placed between the opposing reflecting surfaces within the roof-type reflecting mirror assemblies as shown by the two-dot chain lines in FIG. 5.

FOURTH EMBODIMENT, FIG. 8A, FIG. 813 AND FIG. 8C

The fourth embodiment is for displacing only vertically the optical axis of the viewfinder. Field and eye lenses 22a and 23a may be mounted by lens barrels 22 and 23 respectively which may be made integral with field and eye lens plates and 21 respectively. Alternatively, the lens barrels 22 and 23 may be formed integral with an intermediate plate 24 in the fourth embodiment in order to facilitate the molding of the plates 20, 21 and 24 so that the cost may be reduced. The intermediate plate 24 is further provided with frames 24a, 24b, 24c and 24d extending perpendicular to the plate 24 and the frames 24a and 24b are perpendicular to each other while the frames 24c and 24d are perpendicular to each other as shown.

The frames 24a and 24c have the lens barrels 22 and 23 formed integral therewith while the frames 24b and 24d are provided with apertures 25 and 26 respectively for mounting condenser lenses 25a and 26a respectively. The intermediate plate 24 is further provided with a rectangular aperture 27 for mounting an aperture frame.

Field-lens-side and eye-lens-side plates 20 and 21 are similar in construction so that only the field-lens-side plate 20 will be described. The plate 20 has a hollow hexahedronlike reflecting mirror assembly. In other words, the reflecting mirror assembly consists of two triangular prisms placed together with vertex edges at right angles to each other as shown in FIG. 8-C, so that when both of the reflecting mirror assemblies of the field-lens-side and eye-lens side plates 20 and 21 are assembled, they may look like the combination of two right prisms and one Porro prism as shown in FIG. 3-A. It is, therefore, readily seen that the hypotenuse faces 20a and 20b are made into the reflecting surfaces, as compared with the first three embodiments in which the two side faces are made into the reflecting surfaces. The plates 20, 21 and 24 are provided with holes 28, 28a and 28b respectively for optical alignment in assembly and for securing them together by inserting bolts or the like.

The field-lens-side, eye-lens side and intermediate plates 20, 21 and 24 are assembled as shown in FIGS, 8-A and 8-8 and the beam of light is displaced as indicated by the arrows in FIG. 8-C. That is, the optical axis of the viewfinder is displaced vertically.

What is claimed is:

1. A real image viewfinder employing hollow rooftype reflecting mirror assemblies comprising:

a. a first plate having a first opening therein;

b. a first hollow roof-type reflecting mirror assembly mounted in said first opening;

c. a second plate having a second opening therein;

d. a second hollow roof-type reflecting mirror assembly mounted in said second opening;

e. a field lens for directing light onto said first reflecting mirror assembly;

f. an eye-lens for receiving light reflected from said second reflecting mirror assembly;

g. an intermediate plate interposed between said field lens and said eye-lens and having means thereon for connecting said first and second plates to the opposite faces thereof so that they may be assembled into a unitary construction with one mirror surface of said first reflecting mirror assembly disposed opposite one mirror surface of said second mirror assembly; and

h. means in said intermediate plate permitting the passage of light for reflection by said one mirror surface of said first mirror assembly to said one mirror surface of said second mirror assembly.

2. A real image viewfinder as in claim 1 wherein;

i. said second plate has a lens barrel for mounting said field lens thereon, and said second hollow right-angle-roof-type reflecting mirror assembly is mounted thereon with two inner side faces made into the reflecting surfaces;

j. said first plate has a lens barrel for mounting said eye-lens thereon, and said first hollow right-angleroof-type reflecting mirror assembly is mounted thereon with two inner side faces made into the reflecting surfaces; and

k. said means in said intermediate plate comprises two condenser lenses respectively mounted in optical alignment with said field lens and said eyelens between said lenses and said first and second reflecting mirror assemblies respectively, and an aperture frame mounted between the mirror surfaces of said first and second mirror assemblies in opposed relation.

3. The viewfinder as in claim 2 wherein said first and second reflecting mirror assemblies are so arranged that the optical axis of said viewfinder may be displaced both vertically and laterally.

4. The viewfinder as in claim 2 further comprising the combination of:

I. an exposure meter m. a small aperture formed through a reflecting surface of said second mirror assembly so an indication on said exposure meter may be viewed through said viewfinder together with the image of a subject. 5. The viewfinder as in claim 2 wherein said condenser lenses mounted insaid intermediate plate are so placed as to be perpendicular to the surfaces of said intermediate plate so that said condenser lenses may be disposed within said reflecting mirror assemblies between the opposing reflecting surfaces thereof, respectively.

6. A real image viewfinder as in claim 1 wherein said first plate and said second plate each has a hollow hexahedron reflecting mirror assembly consisting of two regular triangular prisms placed together with their vertex edges at right angles to each other, the two opposed hypotenuse faces of said two regular triangular prisms being made into the reflecting surfaces, and said intermediate plate hasa pair of right angle frames extending perpendicular to the surfaces of said intermediate plate from the opposite sides thereof; one of the side faces of each of said right angle frames extending in the same plane and having condenser lenses mounted therein while the other side faces of each of said right angle frames extend in parallel with each other and have lens barrels formed integral therewith for mounting said field and eye lenses respectively; and with a rectangular aperture in said intermediate plate for mounting an aperture frame between the opposing reflecting surfaces of said first and second reflecting mirror assemblies.

7. The viewfinder as in claim 6 wherein said first and second reflecting mirror assemblies are so arranged as to displace the optical axis of said viewfinder parallel to itself.

8. The viewfinder as in claim 1 wherein said first plate and said first reflecting mirror assembly are interchangable with said second plate and said second reflecting mirror assembly.

9. The viewfinder as in claim 1 wherein said first and second plates are integrally molded from a synthetic resin respectively with the outer surfaces of said first and second reflecting mirror assemblies to form a housing therefor.

10. The viewfinder as in claim 2 wherein said first and second plates have said respective lens barrels molded integrally therewith. 

1. A real image viewfinder employing hollow roof-type reflecting mirror assemblies comprising: a. a first plate having a first opening therein; b. a first hollow roof-type reflecting mirror assembly mounted in said first opening; c. a second plate having a second opening therein; d. a second hollow roof-type reflecting mirror assembly mounted in said second opening; e. a field lens for directing light onto said first reflecting mirror assembly; f. an eye-lens for receiving light reflected from said second reflecting mirror assembly; g. an intermediate plate interposed between said field lens and said eye-lens and having means thereon for connecting said first and second plates to the opposite faces thereof so that they may be assembled into a unitary construction with one mirror surface of said first reflecting mirror assembly disposed opposite one mirror surface of said second mirror assembly; and h. means in said intermediate plate permitting the passage of light for reflection by said one mirror surface of said first mirror assembly to said one mirror surface of said second mirror assembly.
 2. A real image viewfinder as in claim 1 wherein; i. said second plate has a lens barrel for mounting said field lens thereon, and said second hollow right-angle-roof-type reflecting mirror assembly is mounted thereon with two inner side faces made into the reflecting surfaces; j. said first plate has a lens barrel for mounting said eye-lens thereon, and said first hollow right-angle-roof-type reflecting mirror assembly is mounted thereon with two inner side faces made into the reflecting surfaces; and k. said means in said intermediate plate comprises two condenser lenses respectively mounted in optical alignment with said field lens and said eye-lens between said lenses and said first and second reflecting mirror assemblies respectively, and an aperture frame mounted between the mirror surfaces of said first and second mirror assemblies in opposed relation.
 3. The viewfinder as in claim 2 wherein said first and second reflecting mirror assemblies are so arranged that the optical axis of said viewfinder may be displaced both vertically and laterally.
 4. The viewfinder as in claim 2 further comprising the combination of: l. an exposure meter m. a small aperture formed through a reflecting surface of said second mirror assembly so an indication on said exposure meter may be viewed through said viewfinder together with the image of a subject.
 5. The viewfinder as in claim 2 wherein said condenser lenses mounted in said intermediate plate are so placed as to be perpendicular to the surfaces of said intermediate plate so that said condenser lenses may be disposed within said reflecting mirror assemblies between the opposing reflecting surfaces thereof, respectively.
 6. A real image viewfinder as in claim 1 wherein said first plate and said second plate each has a hollow hexahedron reflecting mirror assembly consisting of two regular triangular prisms placed together with their vertex edges at right angles to each other, the two opposed hypotenuse faces of said two regular triangular prisms being made into the reflecting surfaces, and said intermediate plate has a pair of right angle frames extending perpendicular to the surfaces of said intermediate plate from the opposite sides thereof; one of the side faces of each of said right angle frames extending in the same plane and having condenser lenses mounted therein while the other side faces of each of said right angle frames extend in parallel with each other and have lens barrels formed integral therewith for mounting said field and eye lenses respectively; and with a rectangular aperture in said intermediate plate for mounting an aperture frame between the opposing reflecting surfaces of said first and second reflecting mirror assemblies.
 7. The viewfinder as in claim 6 wherein said first and second reflecting mirror assemblies are so arranged as to displace the optical axis of said viewfinder parallel to itself.
 8. The viewfinder as in claim 1 wherein said first plate and said first reflecting mirror assembly are interchangable with said second plate and said second reflecting mirror assembly.
 9. The viewfinder as in claim 1 wherein said first and second plates are integrally molded from a synthetic resin respectively with the outer surfaces of said first and second reflecting mirror assemblies to form a housing therefor.
 10. The viewfinder as in claim 2 wherein said first and second plates have said respective lens barrEls molded integrally therewith. 